| SYSTEMD.DEVICE(5) | systemd.device | SYSTEMD.DEVICE(5) |
.SH "NAME" systemd.device - Device unit configuration
.SH "SYNOPSIS"
.PP device.device
.SH "DESCRIPTION"
.PP A unit configuration file whose name ends in .device encodes information
about a device unit as exposed in the sysfs/udev(7) device tree. This
may be used to define dependencies between devices and other units.
.PP This unit type has no specific options. See systemd.unit(5) for
the common options of all unit configuration files. The common configuration
items are configured in the generic [Unit] and [Install] sections. A
separate [Device] section does not exist, since no device-specific options
may be configured.
.PP systemd will dynamically create device units for all kernel devices that
are marked with the systemd udev tag (by default all block and network
devices, and a few others). Note that if
systemd-udevd.service is not running, no device units will be
available (for example in a typical container).
.PP Device units are named after the /sys/ and /dev/ paths they control.
Example: the device /dev/sda5 is exposed in systemd as dev-sda5.device. For
details about the escaping logic used to convert a file system path to a
unit name see systemd.unit(5).
.PP To tag a udev device, use TAG+="systemd" in the udev rules
file, see udev(7) for details.
.PP Device units will be reloaded by systemd whenever the corresponding
device generates a changed event. Other units can use
ReloadPropagatedFrom= to react to that event.
.SH "AUTOMATIC DEPENDENCIES"
.SS "Implicit Dependencies"
.PP Many unit types automatically acquire dependencies on device units of
devices they require. For example, .socket unit acquire dependencies on the
device units of the network interface specified in BindToDevice=.
Similar, swap and mount units acquire dependencies on the units
encapsulating their backing block devices.
.SS "Default Dependencies"
.PP There are no default dependencies for device units.
.SH "THE UDEV DATABASE"
.PP Unit settings of device units may either be configured via unit files, or
directly from the udev database. The following udev device properties are
understood by the service manager:
.PP SYSTEMD_WANTS=, SYSTEMD_USER_WANTS=
Adds dependencies of type Wants= from the device unit to the specified
units. SYSTEMD_WANTS= is read by the system service manager,
SYSTEMD_USER_WANTS= by user service manager instances. These
properties may be used to activate arbitrary units when a specific device
becomes available.
Note that this and the other udev device properties are not taken into
account unless the device is tagged with the systemd tag in the udev
database, because otherwise the device is not exposed as a systemd unit (see
above).
Note that systemd will only act on Wants= dependencies when a device
first becomes active. It will not act on them if they are added to devices
that are already active. Use SYSTEMD_READY= (see below) to configure
when a udev device shall be considered active, and thus when to trigger the
dependencies.
The specified property value should be a space-separated list of valid unit
names. If a unit template name is specified (that is, a unit name containing
an @ character indicating a unit name to use for multiple instantiation, but
with an empty instance name following the @), it will be automatically
instantiated by the device's sysfs path (that is: the path is escaped and
inserted as instance name into the template unit name). This is useful in
order to instantiate a specific template unit once for each device that
appears and matches specific properties.
.RE
.PP SYSTEMD_ALIAS=
Adds an additional alias name to the device unit. This must be an absolute
path that is automatically transformed into a unit name. (See above.)
.RE
.PP SYSTEMD_READY=
If set to 0, systemd will consider this device unplugged even if it shows up
in the udev tree. If this property is unset or set to 1, the device will be
considered plugged if it is visible in the udev tree.
This option is useful for devices that initially show up in an uninitialized
state in the tree, and for which a changed event is generated the moment
they are fully set up. Note that SYSTEMD_WANTS= (see above) is not
acted on as long as SYSTEMD_READY=0 is set for a device.
.RE
.PP ID_MODEL_FROM_DATABASE=, ID_MODEL=
If set, this property is used as description string for the device unit.
.RE
.SH "OPTIONS"
.PP Device unit files may include [Unit] and [Install] sections, which are
described in systemd.unit(5). No options specific to this file type
are supported.
.SH "SEE ALSO"
.PP systemd(1), systemctl(1), systemd.unit(5),
udev(7), systemd.directives(7)
| systemd 262.2 |